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Staphylococcus aureus (S. aureus) is a pathogen closely associated with foodborne diseases. We prepared a reliable colorimetric sensor to detect S. aureus using click chemical reaction and immunomagnetic separation. Aptamer-functionalized and ALP-labeled Fe 3 O 4 NPs act as separation and signal transduction elements. Under the optimized conditions, the Cu + generated by signal transduction triggers a click chemistry reaction, which causes the aggregation of azides and alkyne-AuNPs and a color change. The net extinction ratio of Δ(A 530 /A 760 ) was linearly correlated with the S. aureus concentration from 10 to 10 6  cfu mL -1 , and the limit detection was 2.4 cfu mL -1 . The recoveries were 91.15 ~ 106.36% for the analysis of spiked food and water samples without pre-enrichment. Therefore, we believe that the detection platform can be easily and accurately used for S. aureus detection, providing a broad prospect for on-site visual detection., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.)

A novel colorimetric immunoassay for the detection of Staphylococcus aureus (S. aureus) based on a combination of immunomagnetic separation and signal amplification via etching-enhanced peroxidase-like catalytic activity of gold nanoparticles (AuNPs) was developed. Nanoconjugates composed of gold and iron oxide nanoparticles were synthesized and further modified with antiS. aureus immunoglobulin Y (IgY), which was used for the selective enrichment and rapid separation of target bacteria in complex matrices. AuNPs functionalized with antiS. aureus aptamer were used as an artificial enzyme which has peroxidase-like catalysis activity. Catalytic activity of AuNPs is inhibited by modifying aptamer. However, catalysis of modified AuNPs remarkably enhanced by hydrogen peroxide etching. Based on collecting unbound modified AuNPs in the supernatant and 3,3',5,5'-tetramethylbenzidine-hydrogen peroxide reporting system, the yellow color of solution decreases linearly with increasing the concentration of S. aureus ranging from 10 to 10 6  cfu/mL. The limit of detection is 10 cfu/mL, and total detection time is 65 min. The recoveries of the S. aureus spiked in food samples are 88.2-119.8%. Schematic illustration of colorimetric method for detection of S. aureus based on the IgY-Fe 3 O 4 /Au nanocomposites as capture probes and apt-AuNPs as artificial enzyme with etching-enhanced peroxidase-like catalytic activity.